Firefox Developers stop supporting add-ons installed via direct copying of files to the extensions directory (/usr/lib/mozilla/extensions/, /usr/share/mozilla/extensions/ or ~/.mozilla/extensions/), processed by all Firefox instances on the system (without being tied to a user) . This method is usually used for pre-installing add-ons in distributions, substituting add-ons at the time of installing an application on the system, or for separately delivering an add-on with its own installer.
In Firefox 73, scheduled for February 11, such add-ons will continue to work, but will be moved from the directory common to all browser instances to individual user profiles, i.e. will be converted to the format used when installing through the add-on manager. Starting with the release of Firefox 74, which is expected on March 10, support for add-ons that are not tied to user profiles will be discontinued.
Developers of add-ons installed without reference to a profile are recommended to switch to their products through the standard catalog of add-ons . To install separately downloaded add-ons manually, you can use the add-on download from file option available in the add-on manager.
The reason for the changes presented is that users have problems with such add-ons - such add-ons are often imposed and activated without the userβs explicit consent. Moreover, since the add-on is not tied to the user profile, the user cannot delete them through the regular add-on manager. Direct add-on copying is also often used to install malicious add-ons in Firefox.
Source: opennet.ru